Actuator Arrangement

ABSTRACT

An actuator arrangement comprises a rotatable shaft, a no-back device operable to apply a braking load to the shaft, a drive arrangement operable to drive the shaft for rotation, and an indicator member, wherein the drive arrangement includes a differential drive operable to drive the indicator member for movement.

This invention relates to an actuator arrangement, and in particular toa linear actuator arrangement of the type including a rotatable shaftupon which is located a translatable nut, a roller or ball screwcoupling being provided therebetween such that rotation of the shaftdrives the nut for translation along the shaft. Such an actuator issuitable for use in a number of applications, for example in driving thethrust reverser cowls or other components of an aircraft between stowedand deployed positions.

The actuators used in driving a thrust reverser cowl typically include aso-called no-back device operable to apply a braking load to theactuator to counter externally applied aiding loads and thereby reducethe risk of uncontrolled movement of the cowls or other components movedusing the actuator. Such no-back devices include friction brakecomponents which wear, in use, and one object of the invention is toprovide an actuator arrangement including a sensor arrangement operableto detect whether or not the no-back device is operating correctly.

According to the present invention there is provided an actuatorarrangement comprising a rotatable shaft, a no-back device operable toapply a braking load to the shaft, a drive arrangement operable to drivethe shaft for rotation, and an indicator member, wherein the drivearrangement includes a differential drive operable to drive theindicator member for movement.

Such an arrangement is advantageous in that, during operation, when thebraking load applied by the no-back device is less than expected andless than the resistance to movement of the indicator member, thedifferential drive will drive the indicator member for movement relativeto the shaft, the movement providing an indication that the no-backdevice is not operating correctly. Preferably, the indicator member ismovable axially of the shaft.

A sensor may be provided, the sensor monitoring the position or movementof the indicator member.

Preferably, stop means are provided to limit movement of the indicatormember. The stop means are important in that, once the indicator memberhas reached the stop means, the differential drive operates to increasethe magnitude of the driving load applied to the shaft.

A translatable nut is conveniently mounted upon the shaft, the nut beingarranged to translate along the shaft upon rotation of the shaft.

A lock arrangement is preferably provided to lock the nut and shaftagainst relative rotation. The lock arrangement preferably includes alock component mounted for axial movement relative to the shaft but heldagainst angular movement relative to the shaft, the lock component beingco-operable with the nut to lock the nut to the shaft and therebyprevent relative rotation therebetween. The drive arrangement ispreferably operable to drive the lock component axially relative to theshaft to release the lock arrangement. The indicator member convenientlyforms part of or is associated with the lock arrangement, for example itmay form the lock component.

According to another aspect of the invention there is provided anactuator arrangement comprising a rotatable shaft, a nut mounted uponthe shaft and translatable along the shaft upon rotation of the shaft,and a lock arrangement operable to lock the shaft and nut againstrelative rotation, the lock arrangement comprising a lock componentmounted upon one of the shaft and the nut for axial movement but heldagainst angular movement relative thereto, the lock component beingco-operable with the other of the shaft and the nut, or a componentassociated therewith, to lock the shaft and nut to one another.

The invention will further be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a view illustrating an actuator arrangement in accordance withone embodiment of the invention; and

FIG. 2 is a diagrammatic view illustrating part of the arrangement ofFIG. 1.

The actuator arrangement illustrated in the accompanying drawingscomprises a shaft 10 which is mounted to a housing 12 and supported bybearings 14 for rotation. Axial movement of the shaft 10 is prevented orlimited by the bearings 14. A nut 16 is mounted upon the shaft 10 by aball screw type coupling 18. The nut 16 is connected to a cowl or othercomponent to be moved by the actuator arrangement, in use, the nature ofthe connection of the nut 16 to the cowl or other component being suchthat the nut 16 is held against angular or rotary motion. It will beappreciated that, in use, rotation of the shaft 10 causes the nut 16 totranslate axially along the shaft 10, the direction of rotary movementof the shaft 10 determining the direction in which the nut 16translates, thus rotation of the shaft 10 drives the cowl or othercomponent for movement.

A no-back device 20 is connected between the shaft 10 and the housing12, the no-back device 20 having a friction brake 22 and being operableto apply a braking load to the shaft 10, resisting rotary movement ofthe shaft 10 in one rotary direction, the no-back device 20 furtherincorporating a ratchet mechanism 24 which is operable to avoid theapplication of the braking load when the shaft 10 is rotated in theopposite direction. A no-back device 20 of this general type isdescribed and illustrated in EP 1378685. Although the illustratedno-back device is of the type incorporating a ratchet mechanism 24, ano-back device of the type in which no such ratchet mechanism isprovided and a braking load is applied in both rotary directions of theshaft 10 could be used, if desired. No-back devices of this and otherforms are well known and the no-back device will not be described infurther detail as the specific design of the no-back device is not ofrelevance to the invention.

The shaft 10 is arranged to be driven for rotation by a drivearrangement 26 including a differential drive 27 in the form of arotatable carriage 28 arranged to be driven by a motor (not shown), forexample via a bevel gear from a synchronising shaft, or via a worm gearor directly by the motor. The carriage 28 carries a plurality of pairsof first planet gears 30 and second planet gears 32, each pair of planetgears 30, 32 being in meshing engagement with one another, as shown inFIG. 2. It is envisaged that three or more pairs of planet gears 30, 32may be provided, but more or fewer may be present. The first planetgears 30 each further mesh with the teeth of a drive gear 34 mountedupon the shaft 10. It should be noted that the second planet gears 32 donot engage the drive gear 34. Rather, the second planet gears 32 are inmeshing engagement with teeth formed on or associated with a secondarydrive gear 36, the first planet gears 30 not cooperating with thesecondary drive gear 36. The differential drive 27 applies the inputdrive load to the drive gear 34 and secondary drive gear 36 in aninverse relationship to the resistance to rotation thereof, ie drive ispreferentially applied to the gear experiencing least resistance torotation at any time.

The secondary drive gear 36 is mounted for rotation within the housing12 by bearings 38, the secondary drive gear 36 being coaxial with, andencircling part of, the shaft 10. The secondary drive gear 36 isprovided, internally, with recesses supporting balls 40 which ride inaxially extending grooves 42 formed in the periphery of a coupling 44,the balls 40 and grooves 42 serving to drive the coupling 44 forrotation with the secondary drive gear 36 whilst permitting the coupling44 to move axially. The coupling 44 is provided with an inwardlyextending formation or series of formations 46 which cooperate with ashallow pitch helical recess 48 formed in the shaft 10 such thatrotation of the secondary drive gear 36 and coupling 44 relative to theshaft 10 drives the coupling 44 for limited axial movement relative tothe shaft 10, the movement being limited by the engagement of theformations 46 with the ends of the recess 48.

A lock and indicator member 50 encircles the shaft 10 and is splinedthereto by formations 52 such that the member 50 is movable axiallyrelative to the shaft 10, the spline formations 52 preventing rotationof the member 50 relative to the shaft 10. A spring 54 is engagedbetween the member 50 and the coupling 44, the spring 54 urging themember 50 to the right, in the orientation illustrated. The member 50includes, at its left-hand most end, in the orientation illustrated, anoutwardly extending flange 56 which is co-operable with a bearing 58carried by the coupling 44 so that the member 50 is held captive to thecoupling 44.

The right-hand most end of the member 50 is shaped to define a pair ofprojections 60 receivable within corresponding recesses 62 formed in thenut 16 in the manner of a dog clutch, when the nut 16 occupies itsleft-hand most, retracted position. When the projections are receivedwithin the recesses 62, it will be appreciated that relative rotationbetween the nut 16 and the member 50 is not permitted.

A sensor 64 is arranged to monitor or sense the position of the member50. The sensor 64 could comprise a proximity sensor of a range of forms,for example a microswitch, capacitance, optical or Hall effect basedsensor could be used. An inductive position sensor is currentlypreferred.

In use, starting from the retracted position in which the nut 16occupies its left-hand most position and the member 50 occupies a lockedposition in which the projections 60 are received within the recesses 62of the nut 16, it will be appreciated that the shaft 10 and nut 16 arelocked to one another against relative rotation as the member 50 is innon-rotatable engagement with both the shaft 10 (by virtue of the splineformations 52) and the nut 16 (by virtue of the dog clutch typecoupling). The actuator arrangement is thus locked against extension.

When extension of the actuator arrangement is required, the carriage 28is driven for rotation. As, at this time, the nut 16 and shaft 10 arelocked to one another against relative rotation and the nut 16 is heldagainst rotation by virtue of its mounting to the cowl or othercomponent with which it is associated, it will be appreciated that theshaft 10 and drive gear 34 are held against rotation. The movement ofthe carriage 28 drives the first planet gears 30, causing them toprecess around the drive gear 34, and the meshing of the planet gears30, 32 of each pair causes the second planet gears 32 to rotate, in turndriving the secondary drive gear 36 for rotation. The rotation of thesecondary drive gear 36 is transmitted to the coupling 44 which, byvirtue of its helical coupling to the shaft 10, moves axially along theshaft 10. The axial movement of the coupling 44 is transmitted to themember 50 which is held captive thereto, retracting the projections 60from the recesses 62, thus releasing the lock between the nut 16 and theshaft 10. The movement of the member 50 is sensed by the sensor 64, thusproviding a signal to the associated circuitry indicating that the lockhas been released.

Continued rotation of the carriage 28 once the lock has been releasedwill result in the coupling 44 continuing to move until the formations46 reach the end of the helical groove 48, the shaft 10 continuing tohave a higher resistance to movement than the lock arrangement due tothe operation of the no-back device 20. However, once the formations 46reach the end of the helical groove 48, the secondary drive gear 36effectively becomes earthed, increasing its resistance to rotation, andso the applied drive is transmitted through the differential drive 27 tothe shaft 10, driving the shaft 10 for rotation against the action ofthe no-back device 20 and causing the nut 16 to translate along theshaft 10, thereby moving the cowl or other component towards itsdeployed position. During this movement, the coupling 44 will remain inits retracted position in which the formations 46 are located at the endof the groove 48 due to the operation of the no-back device 20 applyingits braking load to the shaft 10, resisting the aiding loads applied tothe actuator, in use.

Return movement is achieved by rotating the shaft 10 in the oppositedirection, and this is achieved by reversing the direction of rotationof the carriage 28. Due to external loads, friction and inertia in theactuator and associated components resisting movement of the nut 16 andthus rotation of the shaft 10, the initial rotation of the carriage 28in the retract direction will first be applied through the differentialdrive 27 to the secondary drive gear 36 returning the coupling 44 andmember 50 to their right-hand most positions. Once the formations 46reach the end of the helical groove 48, the secondary drive gear 36effectively becomes earthed again and continued rotation of the carriagewill cause drive to be applied through the differential drive 27 to thedrive gear 34 and shaft 10, returning the nut 16 to its retracted,left-hand most position. During the return of the nut 16 to itsretracted position, the final part of the movement of the nut 16 willpush the member 50 against the action of the spring 54 until theprojections 60 and recesses 62 become aligned, whereon the member 50will return to its locked position under the action of the spring 54,locking the nut 16 and shaft 10 to one another. Where two projections 60and two recesses 62 are provided, the movement of the member 50 againstthe action of the spring 54 will commence just under half a revolutionof the shaft 10 before the nut 16 reaches its retracted position. Thesensor 64 senses the return of the member 50, and can thus output asignal indicating that the actuator arrangement is locked. During thereturn movement, the ratchet mechanism of the no-back device 20 operatesto avoid the application of the braking load to the shaft 10.

If, during the deployment cycle, the no-back device 20 fails or slips,the aiding tensile loading on the shaft 10 will urge the drive gear 34forwards and the motor will be operating to apply a braking torquetending to slow the speed of deployment. Such operation causes thecoupling 44 to be driven relative to the shaft 10 by the differentialdrive 27, the coupling 44 driving the member 50 axially relative to theshaft 10 back towards its locked position. The unexpected movement ofthe member 50 is sensed by the sensor 64 and used by the associatedcontrol circuit to produce a signal indicative of the failure of theno-back device 20 to apply the required braking load.

Although the arrangement described hereinbefore has two projections 60and associated recesses 62, it will be appreciated that more or fewerprojections 60 and recesses 62 may be provided, and that the timing atwhich the nut 16 engages the member 50 to urge it against the action ofthe spring 54, in the event of a no-back failure, will be adjustedaccordingly.

As mentioned hereinbefore, if desired the no-back device 20 may apply abraking load during both extension and retraction of the actuatorarrangement. In such arrangements, no-back failure during either part ofthe operating cycle will give rise to an unexpected movement of themember 50 which will be sensed by the sensor 64 and can be used toprovide a signal indicative of a failure in the no-back device 20.

Although in the arrangement described hereinbefore, the member 50 servesboth as an indicator member for use in sensing the operation of theno-back device 20 and as a lock member of the lock arrangement, it willbe appreciated that separate components may be provided to perform thesefunctions. The function of the indicator member may be provided by, forexample, the coupling 44 or the secondary drive gear 36, if desired.

The arrangement of the invention is advantageous in that it permits theoperation of the no-back device to be monitored, and adjustments made tothe operation of the aircraft to accommodate sensed failures. Further,as a no-back failure can be sensed, it may be possible to use smallermotors and associated drive components than would otherwise be the case.

It will be appreciated that a wide range of modifications andalterations may be made to the arrangement described hereinbeforewithout departing from the scope of the invention.

1. An actuator arrangement comprising a rotatable shaft, a no-backdevice operable to apply a braking load to the shaft, a drivearrangement operable to drive the shaft for rotation, and an indicatormember, wherein the drive arrangement includes a differential driveoperable to drive the indicator member for movement.
 2. An arrangementaccording to claim 1, wherein the indicator member is movable axially ofthe shaft.
 3. An arrangement according to claim 1, further comprising asensor monitoring the position or movement of the indicator member. 4.An arrangement according to claim 1, further comprising stop means tolimit movement of the indicator member.
 5. An arrangement according toclaim 1, further comprising a lock arrangement to lock a nut and theshaft against relative rotation.
 6. An arrangement according to claim 5,wherein the lock arrangement includes a lock component mounted for axialmovement relative to the shaft but held against angular movementrelative to the shaft, the lock component being co-operable with the nutto lock the nut to the shaft and thereby prevent relative rotationtherebetween.
 7. An arrangement according to claim 6, wherein the drivearrangement is operable to drive the lock component axially relative tothe shaft to release the lock arrangement.
 8. An arrangement accordingto claim 5, wherein the indicator member forms part of or is associatedwith the lock arrangement.
 9. An arrangement according to claim 8,wherein the indicator member forms at least part of the lock component.